1. Field of the Invention
Embodiments of the present invention relate generally to valves for controlling flow of a working fluid through it fluid system. In particular, example embodiments of the invention relate to a combination of a ball segment valve and a spring-assisted, dual plate check valve, which together provide redundant or “double-block” sealing to facilitate maintenance of downstream fluid components of the fluid system.
2. Description of the Related Art
In many industrial applications, ball valves and check valves are used to selectively permit and restrict fluid flow through a conduit. Generally, a ball valve includes a curved or spherical member that can be rotated 90 degrees to move the ball valve between open and closed configurations. An opening through the spherical member is aligned with the conduit to open the ball valve, and is rotated out of alignment with the conduit to close the ball valve. The spherical member maintains contact with a pair of annular or circular valve seats that prevent fluid leakage around the spherical member. A check valve, often described as a one-way valve, is placed within the conduit to permit fluid flow in a first direction and to restrict fluid flow in a second opposite direction. Generally, a check valve includes a flapper or other closure member arranged to open in response to fluid pressure applied by a working fluid on a first side thereof and to close in response to fluid pressure on an opposite side.
Both ball valves and check valve have been placed adjacent one another in various applications to prevent unwanted backflow and to provide positive closure of a conduit. One application where this arrangement is generally ineffective is in positive energy isolation. In this application, all potentially hazardous energy sources, such as flammable, hydrocarbon-based working fluids, are identified and isolated to provide a safe environment for performing maintenance or repair activities. One acceptable option for positive energy isolation is known as “double block and bleed.” This term of art is commonly used in the pipeline and petroleum refining industry to describe establishing two positive seals in a conduit and opening a bleed port between the seals. Any leakage of the working fluid past one of the seals is contained by the other seal and may exit through the bleed port.
Although a ball valve by itself may, in some instances, be used to establish the two positive seals for a double block and bleed arrangement, e.g., one seal at each of the two annular valve seats, a check valve is generally ineffective to serve in a double block and bleed arrangement. Because a check valve generally opens in response to a fluid pressure of the working fluid, a sealing force provided by the check valve is generally no greater than a force provided by the pressure of the working fluid. In some applications, this relatively low sealing force is insufficient to provide a safe working environment for welding or other maintenance activities on downstream fluid components. A demand exists for a valve arrangement that at is effective for positive energy isolation and for the prevention of backflow. Also, there is a demand for a valve arrangement that provides redundant closure members within a package that provides weight, space and cost savings over single valves.